During closed mitosis in fission yeast, growing microtubules push onto the nuclear envelope to deform it, which results in fission into two daughter nuclei. The resistance of the envelope to bending, quantified by the flexural stiffness, helps determine the microtubule-dependent nuclear shape transformations. Computational models of envelope mechanics have assumed values of the flexural stiffness of the envelope based on simple scaling arguments. The validity of these estimates is in doubt, however, owing to the complex structure of the nuclear envelope. Here, we performed computational analysis of the bending of the nuclear envelope under applied force using a model that accounts for envelope geometry. Our calculations show that the effective bending modulus of the nuclear envelope is an order of magnitude larger than a single membrane and approximately five times greater than the nuclear lamina. This large bending modulus is in part due to the 45 nm separation between the two membranes, which supports larger bending moments in the structure. Further, the effective bending modulus is highly sensitive to the geometry of the nuclear envelope, ranging from twofold to an order magnitude larger than the corresponding single membrane. These results suggest that spatial variations in geometry and mechanical environment of the envelope may cause a spatial distribution of flexural stiffness in the same nucleus. Overall, our calculations support the possibility that the nuclear envelope may balance significant mechanical stresses in yeast and in cells from higher organisms.

中文翻译：

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核包膜的几何形状决定其抗弯刚度。

在裂变酵母的封闭有丝分裂过程中，不断增长的微管推入核膜，使核膜变形，从而导致裂变成两个子核。外壳抗弯曲的能力（通过抗弯刚度量化）有助于确定微管相关的核形状转变。包络线力学的计算模型已基于简单的缩放参数假定了包络线的弯曲刚度值。但是，由于核被膜结构复杂，这些估计的有效性令人怀疑。在这里，我们使用考虑包壳几何形状的模型对施加力下核包壳的弯曲进行了计算分析。我们的计算表明，核包膜的有效弯曲模量比单个膜大一个数量级，比核薄层大大约五倍。较大的弯曲模量部分归因于两个膜之间的45 nm间隔，这支持了结构中的较大弯矩。此外，有效弯曲模量对核包膜的几何形状高度敏感，范围是对应膜的两倍到一个数量级。这些结果表明，包膜的几何形状和机械环境的空间变化可能会导致同一核中抗弯刚度的空间分布。总体，